The growth of microorganisms in industrial water systems is a never-ending concern for industry. The accumulation of microbiological organisms and their resulting byproducts often interfere with water processing and manufacturing. In the paper industry, the growth of microorganisms in pulp and paper mill waters can adversely affect finished paper products by spoiling the paper furnish, resulting in quality loss and product defects such as holes and spots. In cooling water systems, the growth of microorganisms can lead to deposits of bacterial colonies on metal parts causing their surfaces to corrode and pit. Additionally, systems are adversely affected by microbial growth by reduced efficiency in heat exchangers and fouling which impedes the functionality of the system.
The conventional method of controlling microbial growth is through the use of biocides. Biocides are chemicals that inhibit microbial growth by destroying the cell wall or cellular constituents of microorganisms. Physical conditions such as temperature, radiation, or assimilation with treatment chemicals contained within a system can have a negative impact on the effectiveness of the biocide. To compensate for the reduced effect, biocides can either be added continuously or judiciously on an as required basis. Judicious use of biocides is encouraged since biocides are both expensive and toxic. Thus, to prevent waste, constant monitoring and testing of the water system is required to determine the proper quantity of biocide for controlling microbial growth.
Known techniques to measure the amount of microbiological activity in an industrial water system include grab sampling and plating techniques. Grab sampling is accomplished by removing an aliquot of water from the system and testing said aliquot off-line. Often the subsequent testing is done off-site as well as off-line. Biocide addition to the water system is adjusted depending upon the results of the sampling.
One grab-sample method involves withdrawing a sample, diluting the sample, and applying the sample to the surface of a nutrient agar medium. After incubation for 24 to 48 hours, the sample is checked for the presence of microorganisms and, where appropriate, the organisms are counted by manual or video means. A variation of this method consists of withdrawing a sample and culturing it for a predetermined time, and then observing the culture medium by nephelometry or turbidimetry. In other words, the presence of microorganisms is revealed by the opacity of the culture medium.
A significant problem associated with grab sampling is the time-lag between withdrawing the sample and completing the analysis to determine the level of microbiological activity in the sample. This time lag can be exacerbated when the samples have to be transported off-site for analysis; further delaying obtaining the results.
In addition to grab sampling, other on-site sampling techniques are available, such as Dip slide and Adenosine Triphosphate (ATP) tests. Unfortunately, such tests are not conducive to instantaneous field readings, given that Dip slides require 24 to 48 hours for test results to develop. ATP tests, although capable of giving results in a short (&lt;2 minutes) time, require reagents needing refrigeration and test equipment which is expensive and often not available in the field. Thus, neither test is optimal for field evaluation of microbiological contamination.
Another problem with grab sampling is that it usually underestimates the overall microbiological activity in the industrial water system because grab sampling is only sufficient to provide an indication of the planktonic microbiological activity, not the sessile activity. Planktonic microbiological populations are alive and exist suspended within the water of an water system. Hereinafter, the term "sessile" refer to populations of microorganisms that are alive, but immobile. It is possible to get an industry-acceptable measurement of planktonic populations by grab sampling since planktonic microorganisms are suspended within the water sample that is removed and tested for microorganism concentrations. In contrast, sessile populations are permanently attached to the structures within the system and their presence is not easily measured by removing a sample of water and testing this sample for microorganisms.
Thus, there is a need for a real-time method capable of monitoring both the planktonic and sessile microbial populations in an industrial water system and using that measurement to control the amount of biocide being added to said industrial water system.